Value streams are fundamentally customer-centric; they map the end-to-end flow of work required to deliver value to a customer. Therefore, the most effective way to identify and understand a value stream is to start from the customer's perspective. Mapping the customer journey and their various interactions (touchpoints) with the organization's services provides a clear visualization of the steps, teams, and systems involved in delivering value, thereby defining the value stream that deployment activities must support.

A. Analyzing past failures is a reactive measure used to improve an existing process, not to proactively identify an end-to-end value stream.

C. IT vendors provide components or tools used within a value stream; they lack the holistic, end-to-end organizational view to define it.

D. This is an arbitrary and inefficient method that is not aligned with the ITIL principle of 'Focus on value'.

1. AXELOS. (2020). ITIL® 4: Create, Deliver and Support. Section 3.1.2, "Designing a value stream." This section describes techniques for value stream mapping, which often begin with identifying the service and its consumers.

2. AXELOS. (2020). ITIL® 4: Drive Stakeholder Value. Section 2.3, "Understanding and mapping the customer journey." This section explicitly links mapping the customer journey to understanding how value is co-created and delivered.